Black slug

Black slug
A live and active individual of Arion ater
Conservation status
No special status[1][2]
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
(unranked):	clade Heterobranchia clade Euthyneura clade Panpulmonata clade Eupulmonata clade Stylommatophora informal group Sigmurethra
Superfamily:	Arionoidea
Family:	Arionidae
Genus:	Arion
Species:	A. ater
Binomial name
Arion ater (Linnaeus, 1758)
Synonyms[3]
Limax ater Linnaeus, 1758 Arion empiricorum Férussac, 1819

The black slug, also known as black arion, European black slug, or large black slug, scientific name Arion ater, is a species of large land slug, a terrestrial slug in the family Arionidae, the roundback slugs.

Description

The size of the slug varies from 10 to 15 cm. Maturity is reached at about 2.5 cm.^[4]

The color of the black slug is generally deep black, but the colouration is variable and this slug can even be white. The general trend is for a darker pigmentation the farther north the species is found. The classification of brown-coloured and rust-coloured "black" slugs is somewhat disputed; the brown variation is sometimes considered to be a separate species, Arion rufus (Red Slug).^[4] Young specimens of black slug do have a brown colour, which is later lost if and when the slug changes color to the mature state.^[1]

The foot-fringe is black. The tubercles large and elongate. The sole is blackish grey. Juveniles are ivory whitish with black head, but soon become greyish, half-grown animals are often black like adults.Genitalia:Atrium and vagina considerably narrower than spermatheca, oviduct narrow, spermatheca spherical.^[5]

The slug covers itself in a thick foul-tasting mucus which serves as both protection against predators as well as a measure to keep moist. It is somewhat difficult to wash off.

Like other members of the family Arionidae, the black slug has a pneumostome (breathing hole) on the right side of its mantle through which it breathes. This mantle is the part which in snails secrete a shell, and in this species of slug the mantle contains a resilient protective structure of calcareous granules.^[1]

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  White variant of the black slug Arion ater

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  Brown variant of Arion ater

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  Brown Arion ater

• 

  Colour variants of Arion ater

Distribution

This species is found in northern Europe (including Britain) and the Pacific Northwest.^[1]

• Great Britain
• Ireland
• Germany^[6]
• Canada
  • British Columbia
  • Newfoundland^[7]
  • Quebec (specifically on Mont Bellevue in Sherbrooke)^[8]
• Scandinavia
• United States
  • Oregon
  • Washington
• Gerês, Portugal
• Maladeta Mountains, Spain
• Italy

This species is well-established in Washington and Oregon, and it is considered to represent a potentially serious threat as a pest, an invasive species which could negatively affect agriculture, natural ecosystems, human health or commerce. Therefore it has been suggested that this species be given top national quarantine significance in the USA.^[9]

Behaviour

A black slug on the move.

The black slug is mainly nocturnal and avoids exposure to sunlight. It is omnivorous,^[10] eating carrion, fungi, and vegetation (living and decaying). The slug prefers moist conditions, such as lawns, making it an unwelcome sight for homeowners.^[1] This moist environment is essential for the terrestrial locomotion of the slug to function.

Like all other species of the Arionidae family, the black slug is a hermaphrodite, meaning it can fertilize itself if needed, although a mate is preferred. After mating, the slug lays eggs about 5 mm in diameter. The favoured location for eggs is a dark, cold, damp place such as a compost heap.

In the past two decades, its mating with the non-native (at northern latitudes) pest species Arion vulgaris (or Spanish slug) has resulted in a more resilient hybrid exhibiting increased tolerance to cold.^[11]

Black slug in Northern Poland displaying defensive swaying.

The mucus of the slug is highly distasteful to many animals. However, this slug does have some natural predators, including the hedgehog, badger, shrew, mole, mouse, frog, toad, snake, carnivorous beetle, and some birds.^[12]

When picked up or touched, the black slug will contract to a hemispherical shape and begin to rock from side to side. This defensive behaviour confuses predators, and is unique in the Arionidae family.^[13]

Human use

Arion ater was used as grease to lubricate wooden axle-trees or carts in Sweden.^[14] This use is documented since at least the 18th century.^[14] Although Black slugs are edible (if somewhat unappetising), their consumption is inadvisable partly due to the poisons that are used to control their population in urban areas where they are considered pests, but also as they are carriers of French heartworm (Angiostrongylus vasorum).^[15]

References

External links

Wikimedia Commons has media related to Arion ater.

• Arion ater at Animalbase taxonomy,short description, distribution, biology,status (threats), images
• Arion ater at Encyclopedia of Life images (3 pages)
• "European black slug", Alan Watson Featherstone, Species profile, Trees for Life website, accessed 23 July 2011